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Abstract:

The invention provides an antireflective film and method for making
thereof. The antireflective film includes a transparent substrate with a
hard coat layer thereon. A low refractive index layer having a plurality
of nanoparticles is formed on the hard coat layer. The antireflective
film can increase transmittance and reduce the reflectance thereof
because of the nanoparticles.

Claims:

1. An antireflective film, comprising:a transparent substrate;a hard coat
layer formed on the transparent substrate; anda low refractive index
layer formed on the hard coat layer and comprising a plurality of
nanoparticles having a diameter between 10 nm and 500 nm, therein.

2. The antireflective film as claimed in claim 1, wherein the transparent
substrate comprises glass or polymer.

13. The antireflective film as claimed in claim 1, wherein the hard coat
layer comprises a plurality of microparticles.

14. The antireflective film as claimed in claim 13, wherein the
microparticles comprises silica, alumina, acryl-styrene copolymer,
melamine, or polycarbonate.

15. A method for making an antireflective film, comprising:providing a
transparent substrate;forming a hard coat layer on the transparent
substrate; andforming a low refractive index layer on the hard coat
layer, wherein the the low refractive index layer comprises a plurality
of nanoparticles having a diameter between 10 nm and 500 nm, therein.

19. The method as claimed in claim 15, wherein the hard coat layer
comprises a photoinitiator, an ultraviolet curable resin monomer, an
oligomer, and a solvent.

20. The method as claimed in claim 15, wherein the hard coat layer
comprises a plurality of colloid inorganic nanoparticles or
microparticles.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The invention relates to antireflective films, and in particular
relates to an antireflective film having a plurality of nanoparticles and
method for making thereof.

[0003]2. Description of the Related Art

[0004]Given the rapid development and popularity of electronic devices
such as 3C products, perceptions concerning antireflective films have
changed from `expensive` to `essential`. Today, antireflective films are
required in variety of devices which transmit message through displays,
such as computers, digital cameras, mobile phones, personal digital
assistants (PDA), liquid crystal displays, and optics lenses, to assist
in improving display quality.

[0005]FIG. 1 is a cross section of a conventional antireflective film.
Referring to FIG. 1, a hard coat layer 12 is formed on a transparent
substrate 10 followed by forming a low refractive index layer 14 thereon.
When light passes through the antireflective film including materials
with different refractive indices, a portion of the light is transmitted
while the other portions are reflected. For the reflected light portions,
reflected light waves can result in destructive interference to achieve
antireflection. Generally, antireflective films with many layers, which
have different refractive indices, can achieve better reflectance.
Increasing the layers, however, results in raising fabrication costs and
problems of mechanical strength between the layers, so that fabrication
is more difficult and costly.

[0006]Thus, an antireflective film and method for making thereof
ameliorating the described problems, increasing transmittance and
decreasing reflectance, is needed.

BRIEF SUMMARY OF INVENTION

[0007]Accordingly, the invention provides an antireflective film. An
exemplary embodiment of the antireflective film includes a transparent
substrate, a hard coat layer formed on the transparent substrate, and a
low refractive index layer formed on the hard coat layer having a
plurality of nanoparticles with a diameter between 10 nm and 500 nm.

[0008]Also, the invention provides a method for making an antireflective
film. The method includes providing a transparent substrate and forming a
hard coat layer on the transparent substrate. Then, a low refractive
index layer having a plurality of nanoparticles with a diameter between
10 nm and 500 nm, is formed on the hard coat layer.

[0009]Transmittance and reflectance of antireflective film can be
increased and reduced respectively because of the nanoparticles having
the diameter of around 10 nm to 500 nm. Moreover, because reflectance of
the antireflective film can be reduced without forming extra layers,
fabrication is simplified and costs are reduced.

[0010]A detailed description is given in the following embodiments with
reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0011]The invention can be more fully understood by reading the subsequent
detailed description and examples with references made to the
accompanying drawings, wherein:

[0012]FIG. 1 is a cross section of a conventional antireflective film;

[0013]FIGS. 2A and 2B are cross sections illustrating embodiments and
methods for fabricating an antireflective film; and

[0014]FIG. 3 is a cross section of an antireflective film according to
another embodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

[0015]The following description is the best-contemplated mode for carrying
out the invention. This description is made for the purpose of
illustrating the general principles of the invention and should not be
taken in a limiting sense. The scope of the invention is best determined
by reference to the appended claims.

[0016]The invention will be described with respect to preferred
embodiments in a specific context, namely an antireflective film and
method for making thereof. The invention may also be applied, however, to
other devices requiring an antireflective film. For example, the
antireflective film is disposed in a display device for improving display
quality.

[0017]Referring to FIG. 2A, a transparent substrate 20 is provided.
Preferably, the transparent substrate 20 is made of a material such as
triacetyl cellulose (TAC). However, glass or polymer such as
polyacrylate, polycarbonate, polyethylene, or polyethylene terephthalate
may also be utilized.

[0018]Next, a solution of hard coat layer is prepared. In one embodiment,
100 parts by weight of ultraviolet curable resin is mixed with 100 parts
by weight of solvent such as methyl ethyl ketone (MEK) to prepare the
solution of hard coat layer, also referred to hereafter as a solution of
ultraviolet curable resin. The ultraviolet curable resin may be a
material of polymer including a photoinitiator, an ultraviolet curable
resin monomer, and an oligomer. It is appreciated that the curing time
and hardness of the ultraviolet curable resin relates to formation
between the photoinitiator, the ultraviolet curable resin monomer, and
the oligomer. In this example, a major purpose of the hard coat layer is
to function as a supporting layer for a low refractive index layer later
formed. The ultraviolet curable resin utilized to prepare the hard coat
layer is only required to form a suitable hard layer. Thus, further
description of the formation between the photoinitiator, the ultraviolet
curable resin monomer and the oligomer is not provided.

[0020]After preparation of the hard coat layer solution, the transparent
substrate 20 is then coated with the hard coat layer solution. Next, the
solvent is removed from the hard coat layer solution by baking. The
baking is executed with an oven temperature of around 30° C. to
100° C. for 1 min to 5 mins.

[0021]Alternatively, prior to the step of coating the hard coat layer
solution on the transparent substrate 20, a plurality of colloid
inorganic nanoparticles or microparticles is selectively added to the
hard coat layer solution to decrease shrinkage of the hard coat layer
solution. The colloid inorganic nanoparticles may be a material such as
silica, alumina, zironia, titania, zinc oxide, germanium oxide, indium
oxide, or tin oxide. Preferably, the colloid inorganic nanoparticles have
a diameter of around 10 nanometer (nm) to 50 nanometer (nm). The
microparticles may be a material such as silica, alumina, acryl-styrene
copolymer, melamine, or polycarbonate, and have a diameter of around 1
micrometer (μm) to 10 micrometer (μm).

[0022]After baking, the hard coat layer solution on the transparent
substrate 20 is exposed by ultraviolet light with a dosage of about 500
(mJ/cm2) to form a hard coat layer 22 on the transparent substrate
20, as shown in FIG. 2A. Preferably, the hard coat layer 22 has a
thickness of around 5 μm to 6 μm. It is appreciated that the
thickness of hard coat layer 22 relates to the type of formation and
solid content thereof. Thus, the thickness previously described is only
an exemplary embodiment, is not limited thereto.

[0023]Then, the hard coat layer 22 is placed in a solution of 8% potassium
hydroxide (KOH) at a temperature of about 55° C. for about 2 mins.
Next, the hard coat layer 22 is baked again. Thereafter, a low refractive
index layer is formed on the hard coat layer 22 to form an antireflective
film.

[0024]Examples of antireflective film made and transmittance, haze and
lowest reflectance of the antireflective film tested are described below.

EXAMPLE 1

[0025]After the hard coat layer 22 has been formed, a solution of low
refractive index layer was prepared. 100 parts by weight of low
refractive resin was mixed with 100 parts by weight of isopropyl acetone
and 100 parts by weight of methyl ethyl ketone to prepare the low
refractive index solution (solution A). Next, 30 parts by weight of
nanoparticles was added to the low refractive index solution (solution A)
to form the low refractive index solution having a plurality of
nanoparticles (solution B). 50 parts by weight of the low refractive
index solution having the nanoparticles was further mixed with 80 parts
by weight of methyl ethyl ketone to prepare the low refractive index
solution having the nanoparticles according to Example 1.

[0026]Preferably, the low refractive index resin is a material such as
fluorine-containing silane compound or fluorine-containing copolymer. In
Example 1, the low refractive index resin was fluorine-containing
copolymer Opstar TU2191 produced by JSR. The nanoparticles may be organic
or inorganic. In the example, the organic nanoparticles may be made of a
material such as poly methyl methacrylate (PMMA), polystyrene (PS), or
benzoguanamine. The inorganic nanoparticles may be made of a material
such as silicon oxide, aluminum oxide, antimony-doped tin oxide, tin
oxide, zinc antimonite, antimony pentoxide, indium tin oxide (ITO), or
aluminum-doped zinc oxide.

[0027]Meanwhile, the nanoparticles have a diameter of around 50 nm to 150
nm, preferably around 70 nm to 100 nm. Additionally, the nanoparticles
preferably have a solid content of around 10% to 95%.

[0028]Next, the low refractive index layer solution having the
nanoparticles has been prepared and was then formed by coating on the
hard coat layer 22. A baking step, the same as the step for baking the
hard coat layer 22, was executed to remove the solvent from the low
refractive index layer solution. Thereafter, the low refractive index
solution was exposed to ultraviolet light with a dosage of about 500
(mJ/cm2) to form a low refractive index layer 24 having a plurality
of nanoparticles 26 on the hard coat layer 22, as shown in FIG. 2B.

[0029]Preferably, the low refractive index layer 24 has a thickness of
around 50 nm to 200 nm. It is appreciated that the thickness of the low
refractive index layer relates to the formation and the baking condition.
Thus, the previously described thickness was only an exemplary embodiment
and is not limited thereto.

[0030]Finally, an antireflective film according to Example 1 of the
invention was fabricated. Transmittance, haze and lowest reflectance of
the antireflective film according to Example 1 were measured by a U4100
spectrophotometer produced by Hitachi, and a NDH2000 Haze meter produced
by Nippon Denshoku. The measured results were shown as in Table 1 below.

COMPARATIVE EXAMPLE 1

[0031]100 parts by weight of low refractive index resin, the same as
Example 1, was mixed with 100 parts by weight of isopropyl acetone and
100 parts by weight of methyl ethyl ketone to form a solution of low
refractive index layer (similar to the low refractive index layer
solution in Example 1). The low refractive index layer solution was
coated on the hard coat layer 22 as shown in FIG. 2A. A low refractive
index layer was formed on the hard coat layer by a baking step and an
exposing step using ultraviolet light. An antireflective film according
to Comparative Example 1 was then completed. Note that the baking and the
exposing steps in Comparative Example 1 may be similar to that in Example
1.

[0032]Following formation of the low refractive layer on the hard coat
layer, transmittance, haze and lowest reflectance of the antireflective
film according to Comparative Example 1 were measured by the same
measurement as Example 1. The measured results were shown as in Table 1
below.

EXAMPLE 2

[0033]In Example 2, a low refractive index resin different from the resin
in the Example 1, to prepare a low refractive index layer having a
plurality of nanoparticles. In Example 2, the low refractive index resin
was fluorine-containing copolymer LR204.33A produced by Nissan chemical.

[0034]100 parts by weight of low refractive index resin was mixed with the
nanoparticles to form a low refractive index resin solution (solution C).
Then, 50 parts by weight of the low refractive index resin solution was
mixed with 80 parts by weight of solvent such as methyl ethyl ketone
(MEK) to prepare a low refractive index layer solution.

[0035]The low refractive index layer solution was coated on the hard coat
layer 22 then baked to form a low refractive index layer 24 with
nanoparticles 26 on the hard coat layer 22, as shown in FIG. 2B. In an
exemplary embodiment, the baking step was performed with an oven
temperature of around 60° C. to 100° C. for 5 mins to 60
mins. Following the above described steps, fabrication of an
antireflective film having the nanoparticles, according to Example 2, was
completed.

[0036]Next, transmittance, haze and lowest reflectance of the
antireflective film having the nanoparticles according to Example 2 were
measured by the same measurement devices as Example 1. The measured
results were shown as in Table 1 below.

COMPARATIVE EXAMPLE 2

[0037]In Comparative Example 2, the same low refractive index resin as in
Example 2 was coated on the hard coat layer 22 as shown in FIG. 2A. A
baking step, the same in Example 2 was performed to form a low refractive
index layer without the nanoparticles on the hard coat layer 22 to
complete the antireflective film. Following the above described steps,
transmittance, haze and lowest reflectance of the antireflective film
according to Comparative Example 2 were measured by the same measurement
devices as Example 1 and results were shown as in Table 1 below.

[0038]As shown in Table 1, the antireflective film according to Example 1
had transmittance of about 95.53% and for Comparative Example 1, about
94.41%. Thus, the transmittance of the antireflective film having the
nanoparticles was more than that of the antireflective film without the
nanoparticles. Moreover, the antireflective film according to Example 1
had lowest reflectance of about 0.12% when compared to Example 1, where
lowest reflectance was 1.34%. Thus, the lowest reflectance of the
antireflective film having the nanoparticles was less than that of the
antireflective film without nanoparticles. Accordingly, the
antireflective film with the nanoparticles had relatively higher
transmittance with relatively lowest reflectance.

[0039]Referring to Table 1, the antireflective film according to Example 2
had transmittance of about 94.08% and for Comparative Example 2, about
93.21%. Thus, the transmittance of the antireflective film having the
nanoparticles in Example 2 was higher than the transmittance in
Comparative Example 2. Moreover, in Example 2, the lowest reflectance of
the antireflective film having the nanoparticles was about 0.87%. In
Comparative Example 2, the lowest reflectance of the antireflective film
was about 1.66%. Thus, for lowest reflectance, the antireflective film
having the nanoparticles was less than the antireflective film without
nanoparticles. Accordingly, the antireflective film having the
nanoparticles not only had relatively higher transmittance, but also
relatively lower reflectance.

[0040]In summary, the antireflective film having the nanoparticles
according to the exemplary embodiments of the invention had relatively
higher transmittance, as well as relatively lower reflectance. Moreover,
when the nanoparticles were added, the lowest reflectance of the
antireflective film was reduced to at least twice as much as the one
without them. In the examples of the invention, the lowest reflectance of
the antireflective films was reduced to about 10 times the ones in the
comparative examples.

[0041]Note that the reflectance of the antireflective film according to
the examples of the invention was reduced without forming extra layers.
Thus, fabrication costs were reduced. Meanwhile, fabrication of the
antireflective film having the relatively lower reflectance according to
the invention was simpler.

[0042]In FIG. 3, an antireflective film according to another embodiment of
the invention is shown. The hard coat layer 22 is formed on the
transparent substrate 20. Next, the low refractive index layer 24 having
a plurality of the nanoparticles 26 is formed on the hard coat layer 22
to form an antireflective film with a rough surface. Preferably, the
antireflective film has a surface roughness (Rz) less than 100 nm, so
that its transmittance is increased and reflectance is reduced.

[0043]While the invention has been described by way of example and in
terms of preferred embodiment, it is to be understood that the invention
is not limited thereto. To the contrary, it is intended to cover various
modifications and similar arrangements (as would be apparent to those
skilled in the art). Therefore, the scope of the appended claims should
be accorded the broadest interpretation so as to encompass all such
modifications and similar arrangements.